HSRP Active Active with VPC+ and Anycast HSRP

In this blog I will quickly demonstrate with two similar topologies how HSRP would work in a active active state for HSRP. First using VPC+ and secondly, using Anycast HSRP with multiple Spine switches.

The first requirement for both devices would be to use fabric path. I have Fabric path enabled on all ports connecting from leave to spine. Here is my topology for VPC+. For most of you out there wondering why we need VPC+ with fabric path we need it for the active active. Without it we would only have HSRP on on spine switch.

VPC+This

HSRP is simply running between spine switches I will use VLAN 2 for example.

Spine 1

interface Vlan2
no shutdown
no ip redirects
ip address 10.0.2.1/24
no ipv6 redirects
ip router eigrp 2
ip pim sparse-mode
hsrp version 2
hsrp 2
preempt
priority 110
ip 10.0.2.254

Spine 2
interface Vlan2
no shutdown
no ip redirects
ip address 10.0.2.2/24
no ipv6 redirects
ip router eigrp 2
ip pim sparse-mode
hsrp version 2
hsrp 2
preempt
priority 110
ip 10.0.2.254

vpc domain 1
peer-switch
role priority 100
system-priority 100
peer-keepalive destination 192.168.1.1 source 192.168.1.2 vrf vpcka
delay restore 25
peer-gateway
auto-recovery
delay restore interface-vlan 1
fabricpath switch-id 10
ip arp synchronize

IP ARP Table
Total number of entries: 1
Address Age MAC Address Interface
10.0.2.254 – 0000.0c9f.f002 Vlan2

Now lets check one of the Leaf Switches in the diagram to see how they would get to the mac address of 0000.0c9f.f002.

Keep in mind 1/29 and 1/30 are connected to each Spine switch.

VPC+forwarding

In the show commands you can see traffic going to the HSRP mac will be forwarded over both links through the emulated switch-id. Without the emulated switch-ID traffic would simply forward to one link and one link only. So the emulated switch-ID is sort of a hack on fabric path and VPC to allow this type of behavior.

Alrighty, so now that the easy part is over lets take a look at our new topology!

HSRPanycast

In this example we will use VLAN 4 on the 10.0.4.0/24 subnet. With a HSRP address of 10.0.4.254/24. The config on the HSRP is the same as VLAN 2 however there are some additional configuration items that are different than the normal HSRP config. This needs to be HSRPv2 version 1 will not work.

interface Vlan4
no shutdown
no ip redirects
ip address 10.0.4.2/24
no ipv6 redirects
ip router eigrp 2
hsrp version 2
hsrp 4
ip 10.0.4.254
!
hsrp anycast 4 both
switch-id 40
vlan 4
no shutdown
!
The hsrp mac in this situation is 0000.0c9f.f004. Lets see how the same Leaf switch would forward traffic to get to that mac if a server below it had to talk with its default gateway.

anycastroute

We can see the path can take the previous spine switchs on ports 29 and 30 and also the new one that was added in 17.

Some take aways to Anycast HSRP.

-Needs to be version 2 for HSRP
-This is implimented on the Spine where the L3 should be.
-Needs version 6.2.6 on a 7k and atleast version 7.0 on a 6ks
-I am unsure if this will work with a 55xx with a L3 module.

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